A Syrian military soldier looks a an identification card at a checkpoint on Baghdad Street, in Damascus, Syria, Wednesday, Aug. 21, 2013. Syrian opposition groups claimed scores died on Wednesday in a government offensive near Damascus, attacks in which some activists say regime troops used “poisonous gas.” The government denied the reports. (AP Photo/Hassan Ammar)

UNITED NATIONS — The U.N. Security Council held emergency consultations Wednesday on the latest alleged use of chemical weapons in Syria, and Secretary-General Ban Ki-moon said he is determined to ensure a “thorough investigation” of all reported incidents.

U.N. deputy spokesman Eduardo del Buey said the secretary-general is “shocked” at Wednesday’s alleged use of chemical weapons on the eastern suburbs of Damascus. Syrian anti-government activists accused President Bashar Assad’s regime of carrying out a toxic gas attack that killed at least 100 people, including many children as they slept. The government denied using chemical weapons.

The attack coincided with the visit to Syria by a 20-member U.N. chemical weapons team, led by Swedish expert Ake Sellstrom, which has a mandate to investigate three previous allegations of chemical weapons use.

U.N. Deputy Secretary-General Jan Eliasson was briefing the council on Wednesday’s incident. Council members said they didn’t know if there would be a statement afterward from the U.N.’s most powerful body.

A letter drafted by Britain and France was sent to the secretary-general requesting that the team launch “an urgent investigation ... as expeditiously as possible” into Wednesday’s incident as well. More than half a dozen countries including the United States, Australia, Luxembourg and Germany also signed it, U.N. diplomats said. They spoke on condition of anonymity because contacts have been private.

The letter, obtained by The Associated Press, cited “credible reports of the use of chemical weapons” and urged the secretary-general “to do all you can to ensure that the mission has urgent access to all relevant sites and sources of information.”

A White House spokesman said the U.S. was asking the U.N. to investigate and wants a Security Council debate.

Under the terms of an agreement between the U.N. and the Syrian government, the U.N. team will investigate an alleged chemical weapons attack on March 19 on the village of Khan al Assal outside the city of Aleppo, which was captured by the rebels last month. It will investigate two other sites of alleged attacks, which are being kept secret for security reasons.

Chemical weapons experts have raised doubts about whether investigators will find anything at the three sites because the alleged attacks took place months ago.

Whether the experts are allowed to go to the site of Wednesday’s alleged attack remains to be seen, because it requires approval from the Syrian government.

“Professor Sellstrom is in discussions with the Syrian government on all issues pertaining to the alleged use of chemical weapons, including this most recent reported incident,” del Buey said.

The spokesman said the secretary-general is aware that a number of member states, the Arab League and the European Union have expressed “grave concern” about the latest alleged attack.

“The secretary-general reaffirms his determination to ensure a thorough investigation of the reported alleged incidents that are brought to his attention by member states,” del Buey said.

Diplomats cautioned that the mandate for the current investigation is limited.

The U.N. team will report on whether chemical weapons were used, and if so which ones, but it will not determine the responsibility for an attack. This has led some commentators to question the value of the investigation.

Ban reiterated Wednesday “that any use of chemical weapons, by any side, under any circumstances, would violate international humanitarian law,” del Buey said.

On June 13, the United States said it had conclusive evidence that Assad’s regime had used chemical weapons against opposition forces. That crossed what President Barack Obama had called a “red line” and prompted a U.S. decision to send arms and ammunition to the opposition, though reports say none have arrived yet.